1. Field of the Invention
The invention is directed to a prosthetic kidney, to methods of making the prosthetic kidney and to methods of treating kidney disease with the prosthetic kidney.
2. Description of the Background
The kidneys remove metabolic wastes from the blood, control fluid balance by maintaining homeostasis, and provide important regulatory activities by secreting hormones. Normally about 20% of the blood pumped by the heart is treated by the kidneys.
Nephrons, the functional unit of the kidneys, treat blood by three processes: filtration, reabsorption, and secretion. Each kidney contains about one million nephrons, each consisting of a renal corpuscle and a renal tubule. The shape of a nephron resembles a miniature funnel with a very long convoluted stem. Blood enters the renal corpuscle, through the glomerulus. The filtrate from the blood enters the glomerular capsule, also called Bowman""s capsule, and flows through the renal tubule. The renal tubule comprises four parts, the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and the collecting tubule.
The renal corpuscle comprises a tangled cluster of blood capillaries called a glomerulus which is about 200 microns in diameter surrounded by a thin walled saclike structure called a glomerular capsule. Blood enters and exits the glomerulus through the afferent and the efferent arteriole. While in the glomerulus, blood pressure causes water and various dissolved substances to be filtered out to the glomerular capillaries into the glomerular capsule as glomerular filtrate.
The relative concentration of some of the substances in plasma, glomerular filtrate and urine is shown in Table I and Table II. These values may vary depending on many factors such as fluid consumption, medication, age, diet, health and kidney function of the patient.
The total rate of glomerular filtration typically is about 180 liters per day per person. Most of this volume is returned to the bloodstream via the process of reabsorption. Reabsorption is the movement of substances out of the renal tubules into the blood. Substances reabsorbed comprise water, glucose and other nutrients, sodium and other ions. Reabsorption begins in the proximal convoluted tubules and continues in the loop of Henle, distal convoluted tubules and collecting tubules.
Secretion is the process by which substances and fluids move into the distal and collecting tubules from blood in the capillaries around these tubules. Substances secreted are hydrogen ions, potassium ions, ammonia, and certain drugs. Kidney tubule secretion plays a crucial role in maintaining the body""s acid/base balance.
Homeostasis is maintained by the body by specialized hormones which affect the functions of the kidneys. The pituitary hormone ADH (antidiuretic hormone) decreases the amount of urine produced by making distal and collecting tubules permeable to water. Aldosterone, secreted by the adrenal gland controls the kidney tubules reabsorption of salt and other electrolytes. Primarily, aldosterone stimulates the tubules to reabsorb sodium at a faster rate.
While hormones affect kidney function, the kidneys also produce hormones to regulate the function of other organs. Erythropoietin is a hormone secreted by the kidney cells to regulate the rate of red blood cell formation. Renin, a second hormone secreted by the kidneys regulates blood pressure. In addition, the kidneys activate vitamin D, which is involved in skeletal integrity.
To summarize, blood is treated and urine is formed as a result of glomerular filtration of blood plasma, tubular reabsorption and tubular secretion. In tubular reabsorption, substances such as glucose, amino acids, proteins, creatine, lactic acid, citric acid, uric acid, ascorbic acid, phosphate ions, sulfate ion, calcium, potassium ions, sodium ions water and urea are reabsorbed. In tubular secretion, penicillin, creatinine, histamine, phenobarbital, hydrogen ions, ammonia, and potassium are secreted.
When both kidneys in a patient fail, the blood pressure may rise, fluid may collect in the body, waste levels may build up to a harmful level in the blood and red blood cell production may be reduced. When this happens, treatment is needed to replace the function of the failed kidneys. Treatments for renal dysfunction include hemodialysis, peritoneal dialysis, and kidney transplants.
Hemodialysis is a treatment procedure that cleans and filters the blood of a patient with renal inadequacy. The treatment procedure reduces the levels of harmful wastes, extra salt and fluids. Hemodialysis also helps control blood pressure and maintains the proper balance of chemicals such as potassium, sodium, and chloride in the body.
Hemodialysis uses a dialyzer, or special filter, to treat blood. During treatment, blood from a patient travels through tubes into an external dialyzer. The dialyzer filters out wastes and extra fluids and returns the newly cleaned blood into the body. A typical treatment regimen may comprise three hemodialysis treatments per week for two to four hours each time. During treatment, mobility is limited, but a patient can engage in activities which do not require excessive movements such as reading and writing.
The disadvantages of hemodialysis include side effects and complications caused by rapid changes in the patient""s body fluid and chemical balance during treatment. Muscle cramps and hypotension are two common side effects. Hypotension, a sudden drop in blood pressure, may cause extreme weakness and dizziness.
It usually takes a few months for a patient to adjust to the side effects of hemodialysis. Side effects may be reduced by strict adherence to the proper diet and the consumption of medicines as directed. A proper diet helps to reduce the wastes that build up in a patient""s blood and reduces the load of the kidney. A dietitian is needed to help plan meals according to a physician""s instructions.
Further disadvantages of hemodialysis include high cost and frequent and lengthy travel to a dialysis center. An alternative to dialysis centers is home dialysis. A helper is required for home dialysis and both the patient and the helper require special training. In addition, space is required for storing the machine and supplies at home.
Peritoneal dialysis uses the patient""s abdomen lining, the peritoneal membrane, to filter blood. A cleansing solution, called dialysate, travels through a special tube into the patient""s abdomen. Fluid, wastes, and chemicals pass from tiny blood vessels in the peritoneal membrane into the dialysate. After several hours, the dialysate is drained from the abdomen, taking the wastes from the blood with it. The abdomen is then filled with fresh dialysate and the cleaning process begins again.
The dialysis procedure involves various degrees of difficulties and significant treatment times. While treatment regimens vary, they generally pose significant inconveniences. Typical treatment regimen may comprise, for example, thirty to forty minutes every four to six hours, ten to twelve hours every night, thirty-six to forty-two hours per week, or 24 hour treatment sessions. In addition, special reduced calorie, potassium restricted diets are required in addition to dialysis.
Possible complications of peritoneal dialysis include peritonitis, or infection of the peritoneum. The procedure of peritoneal dialysis comprises many steps where pathogens such as bacteria may be introduced into the body. Symptoms of peritonitis include inflammation, exudations of serum fibrin cells and pus, nausea, dizziness, fever, abdominal pain, tenderness, constipation and vomiting. To avoid peritonitis, care is needed to follow the procedure exactly. A patient needs to be trained to recognize the early signs of peritonitis. Failure to intervene quickly may lead to serious problems.
In addition to short term inconveniences and side effects, hemodialysis and peritoneal dialysis have serious long term complications. Complications such as bone disease, high blood pressure, nerve damage, and anemia may have devastating effects with time. As a result of these complications, 60% of kidney dialysis patients are unemployed and 30% are disabled. Kidney dialysis patients generally have shorter life spans and five fold higher hospitalization when compared to the general population.
Kidney transplantation is a procedure that places a healthy kidney from a donor person into a patient""s body. The implanted kidney augments or replaces the blood filtering load of the patient""s failing kidneys. The implanted kidney is placed between the upper thigh and abdomen. The artery and vein of the new kidney are connected to an artery and vein of the patient, and blood flows through the new kidney and makes urine. The patient""s own kidneys, which may still be partially functional, are not removed, unless they are causing infection or high blood pressure.
Like dialysis, non-histocompatible transplantation is not a cure. Tissue rejection is a significant risk even with a good histocompatibility match. Immunosuppressive regimens to prevent rejection, based on drugs such as cyclosporine, remain the cornerstone of most post-transplantation care. However the pharmaceutical immunosuppressant""s narrow therapeutic window between adequate immunosuppression and toxicity, as determined by the significant intrapatient and interpatient pharmacokinetic and pharmacodynamic variabilities, renders it difficult to discern effective, but minimally toxic immunosuppressive drug levels. Thus, post-transplantation care still incurs significant costs and risks.
Prolonged immunosuppressant consumption may cause side effects. The most serious is a weakened immune system, making it easier for infections to develop. Some drugs also cause weight gain, acne, facial hair, cataracts, extra stomach acid, hip disease, liver or kidney damage. Diets for transplant patients are less limiting than for dialysis patients, but a patient is still required to cut back on some foods. Sometimes even immunosuppressants cannot prevent rejection of the kidney. If rejection happens, patients will be required to employ some form of dialysis and possibly wait for another transplant.
The time it takes to locate a kidney donor varies. There are not enough cadaver donors for every person who needs a transplant and this problem is especially acute in the case of kidney transplants. Another source of kidneys are from living donors such as relatives and spouses. Transplants from genetically related living donors often function better than transplants from cadaver donors because of better histocompatibility.
Humes (U.S. Pat. No. 5,429,938) has reported a method for culturing kidney cells for in vitro tubulogenesis and ex vivo construction of renal tubules. In the method, kidney cells are cultured in the presence of tumor growth factor xcex21, epidermal growth factor and all-trans retinoic acid to form three-dimensional aggregates. Among the disadvantages of the method are the requirements for administration of growth factors and the lack of glomeruli formation. Administration of growth factors to a patient may have unwanted side effects and complications. While Humes disclosed a method which may help regrowth of damaged kidney tissue, a method for construction and use of a prosthetic kidney was not disclosed.
The growth of liver (Rozga et al., Hepatology 17, 258-65) and blood (Schwartz et al., Blood 78, 3155-61) cells constrained in semiporous membrane structures has been reported. These organ structures are not suitable for prosthetic kidney construction because they do not allow for the collection and excretion of glomerular filtrate outside the body.
Naughton and Naughton (U.S. Pat. No. 5,516,680) have reported a three-dimensional kidney cell and tissue culture system. A three-dimensional structure of living stromal cells is laid down on top of a stromal support matrix. Kidney cells are layered on top of this three dimensional system and cultured.
Vacanti and Langer (WO 88/03785) have disclosed methods for culturing cells in a three-dimensional polymer-cell scaffold of biodegradable polymer. Organ cells, cultured within the polymer-cell scaffold, are implanted into a patient""s body to form an artificial organ.
Overall, therefore, it is apparent that the known methods of kidney culture contain inherent defects and flaws and place specific limitations on the ability to use the culture as a prosthetic kidney because of the limitations of their design. While each of these methods has attempted to address some of the problems encountered in the construction of prosthetic kidneys, none of the disclosed methods suggests a method for the construction of an actual prosthetic kidney capable of filtering blood, producing glomerular filtrate, secretion, or reabsorption.
The present invention overcomes the problems and disadvantages associated with current strategies and designs and provides methods, and apparatus for the treatment of kidney dysfunction and failure.
One embodiment of the invention is directed to a prosthetic kidney comprising at least one artificial renal unit (ARU). The artificial renal unit comprises a porous membrane structure having an external surface defining an enclosed internal space having at least one effluent channel, and the membrane structure further having attached to the external surface thereof and in fluid communication with the enclosed internal space thereof a plurality of nephron analogs. Each of the nephron analogs comprises a renal tubule analog having vascularization forming a glomeruli-like structure in at least one region of the renal tubule analog. The renal tubule analog comprises a three-dimensional cell aggregate of kidney tubule cells, the aggregate containing a lumen in fluid communication with the internal space of the membrane structure, and wherein the kidney tubule cells in the aggregate exhibit a brush border.
Another embodiment of the invention is directed to an artificial renal unit comprising a porous membrane structure having an external surface defining an enclosed internal space having at least one effluent channel, and the membrane structure further having attached to the external surface thereof and in fluid communication with the enclosed internal space thereof a plurality of nephron analogs. Each of the nephron analogs comprises a renal tubule analog having vascularization forming a glomeruli-like structure in at least one region of the renal tubule analog. The renal tubule analog comprises a three-dimensional cell aggregate of kidney tubule cells, the aggregate containing a lumen in fluid communication with the internal space of the membrane structure, and wherein the kidney tubule cells exhibit a brush border.
Another embodiment of the invention is directed to an artificial renal unit precursor suitable for implanting in a patient with need of additional renal function comprising a porous membrane structure having an external surface defining an enclosed internal space and having at least one effluent channel. The membrane structure further having attached to the external surface thereof and in fluid communication with the enclosed internal space thereof, a plurality of renal tubule analogs. The renal tubule analogs comprise a three-dimensional aggregate of kidney tubule cells, the aggregate containing a lumen in fluid communication with the internal space of the membrane structure, and wherein the kidney tubule cells in the aggregate exhibit a brush border.
Another embodiment of the invention is directed to a method for making an artificial renal unit precursor suitable for implantation into a patient in need of additional renal function comprising the steps of providing a porous membrane structure having an external surface defining an enclosed internal space having at least one effluent channel; contacting the external surface with a suspension of kidney tissue cells; and culturing the kidney cells on the external surface in vitro to form a plurality of renal tubule analogs, the renal tubule analogs comprising a three-dimensional aggregate of kidney tubule cells, the aggregate containing a lumen in fluid communication with the enclosed space of the membrane structure, and wherein the kidney tubule cells in the aggregate exhibit a brush border.
Another embodiment of the invention is directed to a method for treating kidney disease, or augmenting renal function, in a patient comprising the steps of implanting an artificial renal unit precursor described above into the patient in an area having native vascular supply; inducing the native vascular supply to form glomeruli-like structures at the one region; and connecting the effluent channel from the membrane structure to the urinary system of the patient.
Another embodiment of the invention is directed to a porous membrane structure for a prosthetic kidney comprising, a semipermeable membrane of a biocompatible polymer with an external surface defining an internal space, and wherein the membrane structure comprises a plurality of hollow tubes in fluid communication with a header and an effluent channel on the header allowing drainage of the internal space.
Another embodiment of the invention is directed to a method for making a renal tubule analog comprising the steps of isolating kidney tissue; dissociating the kidney tissue by enzymatic treatment to form a cell suspension; culturing the kidney cell suspension in vitro; treating an enclosed porous membrane structure with extracellular matrix protein; culturing the kidney cells on the treated exterior surface of the enclosed porous membrane structure to form renal tubule analogs, wherein the renal tubule analogs comprise three-dimensional cell aggregates of kidney tubule cells, containing lumens within the interior of the aggregates; and wherein the tubule cells exhibit a brush border.
Other embodiments and advantages of the invention are set forth, in part, in the description which follows and, in part, will be obvious from this description and may be learned from the practice of the invention.